The picture below shows the distribution of air pressure conditions in parts of Asia on a certain day in November. Read the picture and complete questions 3-4. The correct description of the weather conditions in Xi'an is (　) A.

A. Xi'an is located in the high-pressure center, with downdrafts prevailing, so it does not meet the meaning of the question;

B. Xi'an is located in the high-pressure center, with downdrafts prevailing, and the weather is clear, so it does not meet the purpose of the question. Question meaning;

C. Xi'an is located in the high pressure center, where downdrafts prevail, the weather is clear, the temperature varies greatly between days, and frost weather may occur, so it is correct;

D. Xi'an is located in In the high pressure center, downdrafts prevail, the weather is clear, and the temperature varies greatly between days, so it does not meet the meaning of the question.

So choose: C.